Fix unknown GUID 4294967295 in stream statistics

4294967295 (0xffffffff) is actually used internally by Ostinato for the
Total or Aggregate stats. When stream stats are fetched from more than
one portgroups, a kAggrGuid entry was added for each portgroup in the
GUID list. However, the GUI only tags the last row with the kAggrGUID as
the "Total" row.

Fix is to ensure we add kAggrGuid only once to _guidList.

client/streamstatsmodel.cpp

@@ -225,7 +225,7 @@ void StreamStatsModel::appendStreamStatsList(
             guidList_.append(guid);
     }
 
-    if (guidList_.size())
+    if (guidList_.size() && !guidList_.contains(kAggrGuid))
         guidList_.append(kAggrGuid);
 
 #if QT_VERSION >= 0x040600